A turbo-charged internal combustion engine includes additional components and physical processes in both the intake and exhaust stream. On the intake side of the engine, a centrifugal compressor and intercooler are provided and are located between the air cleaner and a throttle valve. On the exhaust side, a turbine and a waste-gate—which defines a parallel exhaust stream path with the turbine—are both located between the exhaust manifold and the catalyst/muffler. It is known to provide an engine management system (EMS) configured to control the operation of a turbo-charged engine. However, such an EMS is conventionally configured to perform its functions with only a minimal amount of additional information, notwithstanding the increased system complexity, in order to maintain reduced costs (i.e., by reducing the number of sensors). Conventionally, the additional sensors added when an engine is turbo-charged are all located on the intake side (e.g., a boost pressure sensor, and a boost temperature sensor). The foregoing lack of sensors on the exhaust side, however, means that the exhaust states, such as exhaust manifold pressure and turbine outlet pressure and temperature, must be estimated. Conventional estimation logic for a turbo-charged engine is substantially more complex than the relatively simple models that are known and adequate for a naturally aspirated engine.
The existing EMS logic for naturally-aspirated engines have models for determining various exhaust manifold states, such as exhaust manifold pressure PEM and exhaust manifold temperature TEM A known use of PEM is as an input for estimating volumetric efficiency (VE), pumping torque and EGR flow as well as for related control. A known use of TEM is for estimation of the pressure drop over the exhaust system, catalyst temperature estimation and control, and exhaust gas recirculation (EGR) flow estimation and control.
The conventional models for determining TEM are the same for a turbo-charged engine as for a naturally aspirated engine. On a turbo-charged engine, the exhaust temperature is the same temperature as the exhaust gas entering the turbine TT,in. However, there is a temperature drop associated with the expansion-work process that occurs across the turbine, while there is no temperature drop due to expansion-work across the waste-gate path. Furthermore, it is unknown what amount of the exhaust gas flows through the turbine, on the one hand, versus how much flows through the parallel waste-gate path, on the other hand. It is desirable to have accurate information regarding the various exhaust manifold states for a variety of purposes, including those described above, and further including control of the waste-gate valve.
One approach taken in the art is described in Schopp et al, Model Based Control Function For Turbo Charged Spark Ignition Engines, Aachener Kolloquium Fahrzeug-und Motorentechnik 2005 (2005) (hereinafter referred to as “Schopp”). Schopp discloses an approach that models the exhaust manifold pressure state by the filling and emptying of the exhaust manifold. The model in Schopp, however, not only requires a so-called compressor characteristic map, which as known is generally available from the turbo-charger manufacturer, the Schopp model also requires the turbine map, which is more difficult to obtain, and is of questionable validity since it is measured at steady-state conditions, while the conditions on a real-world engine are pulsating. Moreover, another disadvantage of the Schopp model is that it may become unstable, especially near its limit of operation, and accordingly special care is required in configuring it for use, which makes any actual implementation challenging.
There is therefore a need for a system and method for modeling a turbo-charged engine that minimizes or eliminates one or more of the problems set forth above.